RECORD-BASED LOGICAL MODELS

 Network Model

Network model was developed with the view to eliminate the problems faced by hierarchical database during 1980s. The network model (defined by the CODASYL specification) organises data using two fundamental constructs, called records and sets. Records contain fields (which may be organised hierarchically, as in the programming language COBOL). Sets define one-to-many relationships between records: one owner, many members. A record may be an owner in any number of sets, and a member in any number of sets.

A network database model is a database model that allows multiple records to be linked to the same owner file. The model can be seen as an upside down tree where the branches are the member information linked to the owner, which is the bottom of the tree. The multiple linkages which this information allows the network database model to be very flexible. In addition, the relationship that the information has in the network database model is defined as many-to-many relationship because one owner file can be linked to many member files and vice versa.

                                                                                                                                                                           Network Model

Advantages of Network Database

Network database offer many advantages other than ones offered by hierarchical database. Some of them are mentioned below:

1. Simplicity: Similar to the hierarchical model, this model is simple and the implementation is effortless.

2. Ability to Manage More Relationship Types: The network model has the ability to manage one-to-one (1:1) as well as many-to-many (N: N) relationships.

3. Flexibility in data access: Data items can be navigated in more than one way providing the much desired flexibility of the data access.

4. Data Integrity: In a network model, there's always a connection between the parent and the child segments because it depends on the parent-child relationship.

5. Data Independence: Data independence is better in network models as opposed to the hierarchical models.

6. Standards: Universal standards have been developed and enforced in these types of databases.

Disadvantages of Network Database

Although network databases displayed significant improvement over hierarchical databases yet they suffered from disadvantages as mentioned:

1. Functional Flaws: Because a great number of pointers is essential, insertion, updates, and deletion become more complex.

2. Lack of Structural Independence: A change in structure demands a change in the application as well, which leads to lack of structural independence.

3. System Complexity: Each and every record has to be maintained with the help of pointers, which makes the database structure more complex.